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Beatty CJ, Ruiz-Lozano RE, Quiroga-Garza ME, Perez VL, Jester JV, Saban DR. The Yin and Yang of non-immune and immune responses in meibomian gland dysfunction. Ocul Surf 2024; 32:81-90. [PMID: 38224775 DOI: 10.1016/j.jtos.2024.01.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2023] [Revised: 01/04/2024] [Accepted: 01/12/2024] [Indexed: 01/17/2024]
Abstract
Meibomian gland dysfunction (MGD) is a leading cause of dry eye disease and one of the most common ophthalmic conditions encountered in eye clinics worldwide. These holocrine glands are situated in the eyelid, where they produce specialized lipids, or meibum, needed to lubricate the eye surface and slow tear film evaporation - functions which are critical to preserving high-resolution vision. MGD results in tear instability, rapid tear evaporation, changes in local microflora, and dry eye disease, amongst other pathological entities. While studies identifying the mechanisms of MGD have generally focused on gland obstruction, we now know that age is a major risk factor for MGD that is associated with abnormal cell differentiation and renewal. It is also now appreciated that immune-inflammatory disorders, such as certain autoimmune diseases and atopy, may trigger MGD, as demonstrated through a T cell-driven neutrophil response. Here, we independently discuss the underlying roles of gland and immune related factors in MGD, as well as the integration of these two distinct mechanisms into a unified perspective that may aid future studies. From this unique standpoint, we propose a revised model in which glandular dysfunction and immunopathogenic pathways are not primary versus secondary contributors in MGD, but are fluid, interactive, and dynamic, which we likened to the Yin and Yang of MGD.
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Affiliation(s)
- Cole J Beatty
- Department of Integrative Immunobiology, Duke University School of Medicine, Durham, NC, USA; Duke Eye Center, Duke University School of Medicine, Foster Center for Ocular Immunology at Duke Eye Center, Durham, NC, USA
| | - Raul E Ruiz-Lozano
- Duke Eye Center, Duke University School of Medicine, Foster Center for Ocular Immunology at Duke Eye Center, Durham, NC, USA
| | - Manuel E Quiroga-Garza
- Duke Eye Center, Duke University School of Medicine, Foster Center for Ocular Immunology at Duke Eye Center, Durham, NC, USA
| | - Victor L Perez
- Duke Eye Center, Duke University School of Medicine, Foster Center for Ocular Immunology at Duke Eye Center, Durham, NC, USA.
| | - James V Jester
- Department of Ophthalmology and Biomedical Engineering, Gavin Herbert Eye Institute, University of California Irvine, Irvine, CA, USA.
| | - Daniel R Saban
- Department of Integrative Immunobiology, Duke University School of Medicine, Durham, NC, USA; Duke Eye Center, Duke University School of Medicine, Foster Center for Ocular Immunology at Duke Eye Center, Durham, NC, USA.
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Luo S, Djotyan GP, Joshi R, Juhasz T, Brown DJ, Jester JV. Modeling meibum secretion: Alternatives for obstructive Meibomian Gland Dysfunction (MGD). Ocul Surf 2024; 31:56-62. [PMID: 38042297 DOI: 10.1016/j.jtos.2023.11.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Revised: 11/07/2023] [Accepted: 11/19/2023] [Indexed: 12/04/2023]
Abstract
PURPOSE While changes in meibum quality are correlated with severity of meibomian gland dysfunction (MGD) and dry eye disease, little is known regarding the mechanics of meibum secretion. The purpose of this study was to develop a finite element model of meibum secretion and evaluate the effect of various factors that might impact meibum delivery to the ocular surface. METHODS A finite element analysis in COMSOL 6.0 was used to simulate the flow of meibum within the gland's terminal excretory duct. Historical normal human meibum rheology data taken over the meibum melting range from fluid (35-40 °C) to solid (25-30 °C) were then used to calculate the minimum yield stress and plastic viscosity of meibum. The effects of meibum melting state, eyelid pressure and terminal duct diameter on meibum flow rates were then systematically investigated. RESULTS The melting state of meibum from liquid to solid was associated with an increase in the minimum yield stress and plastic viscosity that caused an exponential decrease in meibum flow. Modeling also established that there was a linear correlation between meibum flow rate and eyelid pressure needed to express meibum and the 4th power of the terminal duct radius. CONCLUSIONS Our results suggest that changes in the melting state of meibum from fluid to solid, as well as changes in the radius of the terminal excretory duct and the force exerted by the eyelid can lead to dramatic decreases in the flow of meibum. Together these findings suggest alternative mechanisms for meibomian gland obstruction.
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Affiliation(s)
- Shangbang Luo
- Department of Ophthalmology, University of California, Irvine, CA, USA; Department of Biomedical Engineering, University of California, Irvine, CA, USA
| | - Gagik P Djotyan
- Institute for Particle & Nuclear Physics, Wigner Research Center, Budapest, Hungary
| | - Rohan Joshi
- Department of Ophthalmology, University of California, Irvine, CA, USA; Department of Biomedical Engineering, University of California, Irvine, CA, USA
| | - Tibor Juhasz
- Department of Ophthalmology, University of California, Irvine, CA, USA; Department of Biomedical Engineering, University of California, Irvine, CA, USA
| | - Donald J Brown
- Department of Ophthalmology, University of California, Irvine, CA, USA
| | - James V Jester
- Department of Ophthalmology, University of California, Irvine, CA, USA; Department of Biomedical Engineering, University of California, Irvine, CA, USA.
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Honsho M, Fujiki Y. Asymmetric Distribution of Plasmalogens and Their Roles-A Mini Review. MEMBRANES 2023; 13:764. [PMID: 37755186 PMCID: PMC10534842 DOI: 10.3390/membranes13090764] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 08/03/2023] [Accepted: 08/25/2023] [Indexed: 09/28/2023]
Abstract
Plasmalogens are a unique family of cellular glycerophospholipids that contain a vinyl-ether bond. The synthesis of plasmalogens is initiated in peroxisomes and completed in the endoplasmic reticulum. Plasmalogens are transported to the post-Golgi compartment, including endosomes and plasma membranes, in a manner dependent on ATP, but not vesicular transport. Plasmalogens are preferentially localized in the inner leaflet of the plasma membrane in a manner dependent on P4-type ATPase ATP8B2, that associates with the CDC50 subunit. Plasmalogen biosynthesis is spatiotemporally regulated by a feedback mechanism that senses the amount of plasmalogens in the inner leaflet of the plasma membrane and controls the stability of fatty acyl-CoA reductase 1 (FAR1), the rate-limiting enzyme for plasmalogen biosynthesis. The physiological consequences of such asymmetric localization and homeostasis of plasmalogens are discussed in this review.
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Affiliation(s)
- Masanori Honsho
- Department of Neuroinflammation and Brain Fatigue Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8581, Japan
| | - Yukio Fujiki
- Institute of Rheological Functions of Food-Kyushu University Collaboration Program, Kyushu University, Fukuoka 811-2501, Japan
- Graduate School of Science, University of Hyogo, Himeji 671-2280, Japan
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Pan B, Yuan S, Mayernik L, Yap YT, Moin K, Chung CS, Maddipati K, Krawetz SA, Zhang Z, Hess RA, Chen X. Disrupted intercellular bridges and spermatogenesis in fatty acyl-CoA reductase 1 knockout mice: A new model of ether lipid deficiency. FASEB J 2023; 37:e22908. [PMID: 37039784 PMCID: PMC10150578 DOI: 10.1096/fj.202201848r] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Revised: 03/10/2023] [Accepted: 03/24/2023] [Indexed: 04/12/2023]
Abstract
Peroxisomal fatty acyl-CoA reductase 1 (FAR1) is a rate-limiting enzyme for ether lipid (EL) synthesis. Gene mutations in FAR1 cause a rare human disease. Furthermore, altered EL homeostasis has also been associated with various prevalent human diseases. Despite their importance in human health, the exact cellular functions of FAR1 and EL are not well-understood. Here, we report the generation and initial characterization of the first Far1 knockout (KO) mouse model. Far1 KO mice were subviable and displayed growth retardation. The adult KO male mice had smaller testes and were infertile. H&E and immunofluorescent staining showed fewer germ cells in seminiferous tubules. Round spermatids were present but no elongated spermatids or spermatozoa were observed, suggesting a spermatogenesis arrest at this stage. Large multi-nucleated giant cells (MGC) were found lining the lumen of seminiferous tubules with many of them undergoing apoptosis. The immunofluorescent signal of TEX14, an essential component of intercellular bridges (ICB) between developing germ cells, was greatly reduced and mislocalized in KO testis, suggesting the disrupted ICBs as an underlying cause of MGC formation. Integrative analysis of our total testis RNA-sequencing results and published single-cell RNA-sequencing data unveiled cell type-specific molecular alterations underlying the spermatogenesis arrest. Many genes essential for late germ cell development showed dramatic downregulation, whereas genes essential for extracellular matrix dynamics and cell-cell interactions were among the most upregulated genes. Together, this work identified the cell type-specific requirement of ELs in spermatogenesis and suggested a critical role of Far1/ELs in the formation/maintenance of ICB during meiosis.
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Affiliation(s)
- Bo Pan
- Department of Physiology, Wayne State University, School of Medicine, Detroit, Michigan, USA
| | - Shuo Yuan
- Department of Physiology, Wayne State University, School of Medicine, Detroit, Michigan, USA
- Department of Occupational and Environmental Medicine, School of Public Health, Wuhan University of Science and Technology, Wuhan, Hubei, China
| | - Linda Mayernik
- Department of Pharmacology, Wayne State University, School of Medicine, Detroit, Michigan, USA
| | - Yi Tian Yap
- Department of Physiology, Wayne State University, School of Medicine, Detroit, Michigan, USA
| | - Kamiar Moin
- Department of Pharmacology, Wayne State University, School of Medicine, Detroit, Michigan, USA
| | - Charles S. Chung
- Department of Physiology, Wayne State University, School of Medicine, Detroit, Michigan, USA
| | - Krishnarao Maddipati
- Department of Pathology, Wayne State University, School of Medicine, Detroit, Michigan, USA
| | - Stephen A. Krawetz
- Department of Obstetrics & Gynecology, Wayne State University, Detroit, Michigan, USA
- Center for Molecular Medicine and Genetics, School of Medicine, Wayne State University, Detroit, Michigan, USA
| | - Zhibing Zhang
- Department of Physiology, Wayne State University, School of Medicine, Detroit, Michigan, USA
- Department of Obstetrics & Gynecology, Wayne State University, Detroit, Michigan, USA
| | - Rex A. Hess
- Comparative Biosciences, College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Xuequn Chen
- Department of Physiology, Wayne State University, School of Medicine, Detroit, Michigan, USA
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Honsho M, Fujiki Y. Regulation of plasmalogen biosynthesis in mammalian cells and tissues. Brain Res Bull 2023; 194:118-123. [PMID: 36720320 DOI: 10.1016/j.brainresbull.2023.01.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2022] [Revised: 01/08/2023] [Accepted: 01/27/2023] [Indexed: 01/29/2023]
Abstract
Plasmalogens are a unique family of cellular glycerophospholipids that contain a vinyl-ether bond. Synthesis of plasmalogens is initiated in peroxisomes and completed in the endoplasmic reticulum. The absence of plasmalogens in several organs of patients with deficiency in peroxisome biogenesis suggests that de novo synthesis of plasmalogens contributes significantly to plasmalogen homeostasis in humans. Plasmalogen biosynthesis is spatiotemporally regulated by a feedback mechanism that senses the amount of plasmalogens in the inner leaflet of the plasma membrane and regulates the stability of fatty acyl-CoA reductase 1 (FAR1), the rate-limiting enzyme for plasmalogen biosynthesis. Dysregulation of plasmalogen synthesis impairs cholesterol synthesis in cells and brain, resulting in the reduced expression of genes such as mRNA encoding myelin basic protein, a phenotype found in the cerebellum of plasmalogen-deficient mice. In this review, we summarize the current knowledge of molecular mechanisms underlying the regulation of plasmalogen biosynthesis and the link between plasmalogen homeostasis and cholesterol biosynthesis, and address the pathogenesis of impaired plasmalogen homeostasis in rodent and humans.
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Affiliation(s)
- Masanori Honsho
- Department of Neuroinflammation and Brain Fatigue Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
| | - Yukio Fujiki
- Institute of Rheological Functions of Food-Kyushu University Collaboration Program, Kyushu University, Fukuoka, Japan; Graduate School of Science, University of Hyogo, Hyogo, Japan.
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Butovich I, Yuksel S, Wilkerson A. Probing dietary triacylglycerol metabolism and meibogenesis in mice: A stable isotope-labeled tracer LC-MS/MS study. J Biol Chem 2023; 299:103046. [PMID: 36822324 PMCID: PMC10070659 DOI: 10.1016/j.jbc.2023.103046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 02/10/2023] [Accepted: 02/12/2023] [Indexed: 02/25/2023] Open
Abstract
Exocrine Meibomian glands (MGs) play a central role in the ocular physiology and biochemistry by producing in situ and, mostly, de novo, a secretion (meibum), which is composed of a complex mixture of homologous lipids of various classes, in a metabolic pathway termed meibogenesis. Recent in vivo experiments with a number of mouse models demonstrated that inactivation of any of the major genes of meibogenesis led to alterations in the lipid composition of meibum and severe ocular and MG abnormalities that replicated various human ocular pathologies. However, the role of dietary lipids in meibogenesis, and in the onset and/or alleviation of these diseases, remains controversial. To uncover the role of dietary lipids, the metabolic transformations of a dietary lipid tracer - stable isotope-labeled glyceryl tri(oleate-1,2,3,7,8-13C5) (13C15-TO) - were investigated using LC-high-resolution TOF-MS/MS. We demonstrated that major metabolic transformations of the tracer occurred in the stomach and small intestines where 13C15-TO underwent immediate and extensive transesterification into 13C5- and 13C10-substituted triacylglycerols of various lengths, giving a mixture of 13C-labeled compounds that remain virtually unchanged in the mouse plasma, liver, and white adipose tissue, but were almost undetectable in the feces. Importantly, the tracer and its metabolites were virtually undetectable in MGs, even after 4 weeks of daily supplementation. Notably, unbiased Principal Component Analysis of the data revealed no measurable changes in the overall chemical composition of meibum after the treatment, which implies no direct effect of dietary triacylglycerols on meibogenesis, and left their systemic effects as the most likely mechanism.
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Affiliation(s)
- IgorA Butovich
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, TX, USA; The Graduate School of Biomedical Sciences, University of Texas Southwestern Medical Center, Dallas, TX, USA.
| | - Seher Yuksel
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Amber Wilkerson
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, TX, USA
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Tamura Y, Sassa T, Nishizawa T, Kihara A. Incomplete Elongation of Ultra-long-chain Polyunsaturated Acyl-CoAs by the Fatty Acid Elongase ELOVL4 in Spinocerebellar Ataxia Type 34. Mol Cell Biol 2023; 43:1-17. [PMID: 36748939 PMCID: PMC9980445 DOI: 10.1080/10985549.2023.2169563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Revised: 11/24/2022] [Accepted: 01/11/2023] [Indexed: 02/08/2023] Open
Abstract
Spinocerebellar ataxias (SCAs) are autosomal dominant diseases characterized by cerebellar atrophy and ataxia. The SCA subtype SCA34 is caused by specific mutations in the gene ELOVL4, which encodes a fatty acid (FA) elongase that synthesizes ultra-long-chain (ULC; ≥C26) FAs. However, the pathogenesis and molecular mechanism that confers dominant inheritance remains unknown. Here, a cell-based assay demonstrated that each of the five known SCA34 mutants produced shorter ULC polyunsaturated FA-containing phosphatidylcholines (ULC-PCs) than wild-type protein, in the following order of severity: Q180P and T233M > W246G > I171T and L168F. Next, we generated knock-in mouse embryonic stem cells that contained heterozygous Q180P, heterozygous W246G, or homozygous W246G mutations. Neuronal differentiation-dependent production of ULC-PCs was reduced in heterozygous Q180P and homozygous W246G cells relative to control cells, and we observed shortening of the FA moiety in all mutant cells. This FA shortening was consistent with our prediction that amino acid residues substituted by SCA34 mutations are located in the transmembrane helices that interact with the ω-end region of the FA moiety of the substrate acyl-CoA. Hence, reduced levels and shortening of ULC-PCs in neurons may cause SCA34, and incomplete elongation of ULC polyunsaturated acyl-CoAs by mutated ELOVL4 may induce dominant inheritance.
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Affiliation(s)
- Yuka Tamura
- Laboratory of Biochemistry, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan
| | - Takayuki Sassa
- Laboratory of Biochemistry, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan
| | - Takumi Nishizawa
- Laboratory of Biochemistry, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan
| | - Akio Kihara
- Laboratory of Biochemistry, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan
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Hamada Y, Sasaki L, Uehara H, Suzuki T, Kinoshita S, Otsuka K, Kihara A, Yamaguchi Y, Miyake T, Doi M. Optimising the method for visualising mouse meibomian gland using eyelid whole-mount lipid staining. Ocul Surf 2022; 26:268-270. [DOI: 10.1016/j.jtos.2022.10.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 09/30/2022] [Accepted: 10/03/2022] [Indexed: 12/05/2022]
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Chen CT, Shao Z, Fu Z. Dysfunctional peroxisomal lipid metabolisms and their ocular manifestations. Front Cell Dev Biol 2022; 10:982564. [PMID: 36187472 PMCID: PMC9524157 DOI: 10.3389/fcell.2022.982564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 08/17/2022] [Indexed: 11/13/2022] Open
Abstract
Retina is rich in lipids and dyslipidemia causes retinal dysfunction and eye diseases. In retina, lipids are not only important membrane component in cells and organelles but also fuel substrates for energy production. However, our current knowledge of lipid processing in the retina are very limited. Peroxisomes play a critical role in lipid homeostasis and genetic disorders with peroxisomal dysfunction have different types of ocular complications. In this review, we focus on the role of peroxisomes in lipid metabolism, including degradation and detoxification of very-long-chain fatty acids, branched-chain fatty acids, dicarboxylic acids, reactive oxygen/nitrogen species, glyoxylate, and amino acids, as well as biosynthesis of docosahexaenoic acid, plasmalogen and bile acids. We also discuss the potential contributions of peroxisomal pathways to eye health and summarize the reported cases of ocular symptoms in patients with peroxisomal disorders, corresponding to each disrupted peroxisomal pathway. We also review the cross-talk between peroxisomes and other organelles such as lysosomes, endoplasmic reticulum and mitochondria.
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Affiliation(s)
- Chuck T. Chen
- Department of Nutritional Sciences, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada
| | - Zhuo Shao
- Post-Graduate Medical Education, University of Toronto, Toronto, ON, Canada
- Division of Clinical and Metabolic Genetics, the Hospital for Sick Children, University of Toronto, Toronto, ON, Canada
- The Genetics Program, North York General Hospital, University of Toronto, Toronto, ON, Canada
| | - Zhongjie Fu
- Department of Ophthalmology, Boston Children’s Hospital, Harvard Medical School, Boston, MA, United States
- *Correspondence: Zhongjie Fu,
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Butovich IA, Wilkerson A. Dynamic Changes in the Gene Expression Patterns and Lipid Profiles in the Developing and Maturing Meibomian Glands. Int J Mol Sci 2022; 23:7884. [PMID: 35887230 PMCID: PMC9321132 DOI: 10.3390/ijms23147884] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2022] [Revised: 07/11/2022] [Accepted: 07/13/2022] [Indexed: 11/30/2022] Open
Abstract
Meibomian glands (MGs) and their holocrine secretion-meibum-play crucial roles in the physiology of the eye, providing protection from environmental factors and desiccation, among other functions. Importantly, aging was implicated in the deterioration of the morphology and functions of MGs, and the quantity and quality of meibum they produce, leading to a loss of its protective properties, while the meibum of young individuals and experimental animals provide ample protection to the eye. Currently, the molecular mechanisms of meibum biosynthesis (termed meibogenesis) are not fully understood. To characterize the physiological changes in developing and maturing MGs, we studied the lipidomes and transcriptomes of mouse MGs ranging from newborns to adults. The results revealed a gradual increase in the critical genes of meibogenesis (such as Elovl3, Elovl4, Awat2, and Soat1, among others) that positively correlated with the biosynthesis of their respective lipid products. The MG transcriptomes of young and adult mice were also analyzed using single-cell RNA sequencing. These experiments revealed the existence of multiple unique populations of MG cells (meibocytes, epithelial cells, and others) with specific combinations of genes that encode meibogenesis-related proteins, and identified clusters and subclusters of cells that were tentatively classified as meibocytes at different stages of differentiation/maturation, or their progenitor cells. A hypothesis was formulated that these cells may produce different types of lipids, and contribute differentially to the Meibomian lipidome.
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Affiliation(s)
- Igor A. Butovich
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9057, USA;
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